The Panama Canal Miraflores locks and museum is a must-see but you only need a few hours unless you really want to sit there and watch ships pass through all day. We didn't see any because we were there in the afternoon during a several hour lull in the ship traffic. It's still cool to see the size of it all but I didn't need to watch a ship go through it. I know how such things work and have ridden in a smaller boat through a smaller set of locks before so I'm sure it's just much bigger and much slooowwweeeerrrrr.
The same day we visited the Biomuseo. The building is a new super cool structure designed by Frank Gehry. The exhibit was cool but it was a little underwhelming because they have a whole other half of it that will be even neater in the future. They have models showing how great it will be on display in the huge area where it will be. This new area overlooks what will be a really awesome garden outside which is still under construction. Otherwise, it is a great destination that will be better in the future instead of just a couple of hour smaller thing.
We could have continued past the Biomuseo to the connected islands and had one very full day there if we had known about it that day. We found it another day and also a great seafood restaurant called Sirena. The Punta Culebra Nature Center isn't too big either but it has a nice collection of animals. I liked the frogs and the ever elusive sloths slow-motion hanging around high in the trees like they do in Venezuela. They're hard to spot here too.
the sloth was grooming in their only speed of slow-motion